The present invention finds application particularly in third-generation networks of Wideband Code Division Multiple Access (WCDMA) type. However, the techniques may be applicable also in connection with other types of radio networks, such as GSM, CDMA etc.
In radio telecommunications networks a base station or a node B as it is named in WCDMA provides a radio, or air interface to a mobile user terminal, or user equipment. This radio interface is called the Uu interface in WCDMA. The node B is connected to a Radio Network Controller (RNC) which is the network element responsible for control of radio resources in the Universal Mobile Telephony Network (UMTS) Radio Access Network (UTRAN). The Node B and the RNC are connected through the lub interface. The RNC is in turn connected to a Core Network (CN) which may comprise a number of different network nodes, such as MSC/VLR, SGSN etc.
In third-generation radio access networks increased transmission rates has been a primary goal and new protocols and techniques for achieving increased transmission rates has been developed. A High Speed Downlink Packet Access (HSDPA) protocol has been standardised in WCDMA release 5, and recently it has been complemented by a High Speed Uplink Packet Access (HSUPA) protocol in WCDMA release 6.
In HSUPA different user equipment is assigned different transmission rates, or Grants, ranging from 0 kbps up to 5.76 Mbps. That is, one user may have a larger Grant than another. To support the transmissions, hardware in Node B is allocated in hardware pools and hardware resources are allocated to a particular user to support the transmission rate required. The larger the transmission rates, the more hardware resources required, as well as air interference generated in the Uu interface, and load on the Iub link.
When an Enhanced Direct Channel (E-DCH) user, that is a user having a grant for HSUPA transmission, is in handover more than one cell receives the uplink data transmission from the user equipment. The data received from the different cells are combined in the RNC. However, if the cells belong to the same RBS it is possible, but not necessary, that the combining is performed at the RBS. For E-DCH the RBS will only relay the data to the RNC if the RBS has received the data correctly. Thus, the RNC is responsible to combine the data it receives from all RBSs and cells in the handover. One of the RBS nodes, most likely the node having the best radio characteristics, is a serving node and the other RBS nodes are non-serving nodes.
The serving node can, by sending absolute grants (AG) or relative grants (RG), adjust the scheduled transmission rate for the user equipment, that is, the serving RBS can both increase and decrease the scheduled rate, while the non-serving node can only send relative grants to reduce the transmission rate. There is no communication between the two RBS nodes, so the serving node does not have information relating to the particular capacity circumstances for the non-serving node.